Should I use solder or glue?

You usually only need one or the other. Really it's whatever you like. I personally like primer better, but it is up to you. Try both and see which one...

A good quality regular super glue, or better yet, a gel glue like Loc-Tite. Tiger glue is also good quality.

Yes, you can use a strong glue or perhaps resin, but it won't be as strong or hardy as solder.

Press the iron firmly against the antler. Hold it there for a few minutes and then let go.

Yes, but it's not really worth it since you will be adding shaving cream. The lotion, shaving cream, and foaming hand wash will make the glue look white, instead of...

You can use clear glue, or any type of liquid craft glue. If you use a glue stick you will have to microwave it.

Any glue will do. It is best not to use glue sticks as that glue isn't very sticky. PVA glue, craft glue, super glue or hot glue would work well....

Use a good glue stick as that won't seep through the page and ruin your drawing (it doesn't wet the page like liquid).

Tape will not last as long as glue, especially a glue made for paper. There's no reason you can't use origami paper, though.